(1) Field of the Invention
The present invention relates to a multi-layer optical disk having plural recording layers, more specifically, to an optical disk apparatus capable of stably performing a layer jump, a focus control method and an optical disk.
(2) Description of the Related Art
A multi-layer optical disk having plural recording layers is required of an operation in which an object lens shifts to change (or switch) recording/reproducing layers and a focus position is changed from one layer to another layer (layer jump). In general, a DVD disk has a standardized double recording layer structure. In addition, a number of technologies are available in regard to the layer jump for disks having at least three recording layers.
Japanese Patent Laid-Open Publication No. 2003-123272 discloses an acceleration and deceleration treatment involving a layer jump from a first layer to a third layer, interlacing a second layer, and a deceleration control method on the basis of a focus error signal output from the third layer.
Japanese Patent Laid-Open Publication No. 2004-192784 discloses a high-precision control of a layer jump for a three-layer BD using an objective lens with a high NA (numerical aperture) of at least 0.8. Since a permitted limit of the focal length of such object lens is very narrow, a deceleration treatment on the layer jump is divided into a first acceleration and a second acceleration.
In addition, Japanese Patent Laid-Open Publication No. 2002-304746 discloses a technology for controlling the timing of an acceleration voltage (pulse) and a deceleration voltage (pulse) during a layer jump in a multilayer disk, each layer having different characteristics, is controlled based on the intensity of 2-layer reflected light.